1. Field
An aspect of the present invention relates to a secondary battery.
2. Description of the Related Art
Recently, the use of electronic devices such as cellular phones and notebook computers has increased, and batteries are built in the electronic devices so that it is easy to transport and use the electronic devices. In view of economical efficiency, rechargeable secondary batteries are widely used as the power source for electronic devices. Representative secondary batteries are exemplified by a nickel-cadmium battery, a nickel-hydrogen battery, a lithium ion secondary battery, and the like. Particularly, a lithium secondary battery is widely used because its operating voltage is about three times higher than a nickel-cadmium battery or nickel-hydrogen battery, and its energy density per weight is high.
Since the deterioration or heat generation of a lithium ion secondary battery may be caused by overcharge or overdischarge, the maximum/minimum voltage or temperature of the lithium ion secondary battery is necessarily controlled. Accordingly, a protection circuit module including a secondary protection element is provided to the lithium ion secondary battery. For example, generally used secondary protection elements are a field effect transistor (FET), a positive temperature coefficient (PCT) element, a control integrated circuit (IC), and the like. Since these secondary protection elements are weak against external impact or heat, they may be easily damaged. Therefore, caution is required in manufacturing and handling of these secondary protection elements. Since electronic devices have become light weight and compact, it is difficult to sufficiently protect secondary batteries from external impact using only outer casings of these electronic devices. Therefore, it is desired to develop a secondary battery including a case for a protection circuit module, in which the damage of the protection circuit module can be prevented by the secondary battery itself, and whose manufacturing cost can be reduced.